(1) Field of the Invention
The present invention pertains to an apparatus employed in grounding the stator and end plates of a dynamoelectric device. In particular, the invention pertains to a terminal block constructed of an electrically insulating material and a ground connector constructed of a electrically conductive material that is installed in the terminal block, where the ground connector has a plug projecting from the terminal block at one end and a tab with a fastener hole at its opposite end. Attachment of the terminal block to the stator of the device simultaneously positions the tab of the ground connector with the tab hole aligned with fastener holes of the stator and at least one end plate of the device where assembling the stator and end plate together by a threaded fastener also secures the tab of the ground connector between the stator and end plate.
(2) Description of the Related Art
A dynamoelectric device is often constructed with a ground system that directs electrical energy away from the device in the case of an electric malfunction in the device that could shock a person touching the device or its supporting equipment. In a typical electrical device the ground is attached to an external frame or housing of the device. This insures that in the event of a power supply wire making contact directly or indirectly with the frame or housing of the device that is accessible to a person using the device, the electric energy can be directed away from the housing of the device. By directing the electric energy to a ground a xe2x80x9cshort circuitxe2x80x9d condition is created where the electric energy is directed away from the device along the path of least resistance, thus preventing any person contacting the device from receiving an electrical shock. The high current flow through the ground in situations such as this will often cause self-actuating protective switches in the device to open the circuit and stop electrical current flow to the device. This protects both the device from a high current surge and also protects people who may otherwise contact the malfunctioning device and receive a shock.
In electrical devices such as electric motors installed in household appliances, the external frame of the device is required to be provided with a ground connection to protect persons using the appliance if an electrical malfunction occurs. The ground connection is often directed to a water pipe of the home or the ground pole in a three prong plug electrical socket. Because the electric motor is typically mounted directly to the metallic structure of the appliance, the ground connection is directly to the frame of the motor. In the event of an electric malfunction in the motor, the electric current is directed to the grounding system and people using the appliance are protected from receiving an electrical shock. Grounding of electrical devices in this manner is common. For the purpose of explaining the subject matter of the invention, the example of a small electric motor is used. However, it should be understood that the example is illustrative only and that the grounding system of the invention may be employed in many different types of electrical devices and is not intended to be limited to use with only electric motors.
FIG. 1 is a side elevation view of a typical electric motor 10. The motor is basically comprised of a stator assembly 12, a pair of end plates 14, 16 secured to opposite end surfaces of the stator assembly 12, and a rotor (not shown) mounted on a rotor shaft 18 which in turn is mounted for rotation in a pair of bearings (not shown) mounted in the two end plates 14, 16. A terminal block 20 constructed of an insulating material is mounted on the stator assembly 12. The terminal block 20 has a series of electrical plugs 22 projecting from the block that are connected to the wiring of the stator assembly 12 and provide external connections to the circuitry of the appliance or other device with which the motor is used. The motor also comprises a ground connector 24 that is easily accessible for connection to a conductor used to connect the motor to an external ground, such as the earlier example of the water pipe. The ground connector 24 is secured and grounded to both the stator assembly 12 and one of the two end plates 14 of the motor by the bolt 26 and nut 28 threaded fasteners that secure the end plates 14, 16 to the opposite end surfaces of the stator assembly 12.
FIG. 2 shows the stator 30 removed from the stator assembly 12 of the motor shown in FIG. 1. The stator 30 in this example is comprised of a stack of laminate plates that each have the same, generally square peripheral edge 32. The peripheral edges 32 of each of the plates in the stator stack forms a portion of the motor frame or exterior surface of the motor. The stator has a generally cylindrical center bore 34 surrounded by a plurality of stator poles 36. Four fastener holes 38 pass entirely through the stator stack adjacent the four corners of the stator. The stator fastener holes 38 are positioned on the stator so that they will align with four fastener holes 40 in each of the end plates 14, 16 when the end plates are positioned on the opposite end surfaces of the stator. The stator also has two pairs of terminal block mounting post holes 42 adjacent opposite ends of the stator. The mounting post holes 42 are provided in pairs on opposite sides of the stator to enable a single terminal block to be mounted on either side of the stator or a pair of terminal blocks mounted on the opposite sides of the stator if needed. The mounting post holes 42 are dimensioned to receive mounting posts 44 of the terminal block 20 and to hold the terminal block securely against one of the end surfaces of the stator adjacent the post holes. Typically, the ground connector 24 is also mounted on the end surface of the stator adjacent the terminal block 20. This provides all of the electrical connections to the motor on one side of the motor. As seen in FIG. 2, the ground connector 24 has a plug 46 at one end that projects from a grounding tab 48. The tab 48 has a hole 50 therethrough that is dimensioned to be the same size as the stator fastener holes 38 and the end plate fastener holes 40.
Generally describing the assembly of a motor such as that shown in FIG. 1 and the attachment of the prior art ground connector 24 to the motor, after the stator poles 36 are wound, the winding connections from the stator poles and other circuitry of the motor are made to the conductor plugs 22 of the terminal block 20. The terminal block 20 is then mounted on the end surface of the stator assembly 12 by inserting its posts 44 into the mounting post holes 42 of the stator. The rotor assembly is then inserted into the stator bore. The rotor is supported in the stator bore by inserting the opposite ends of the rotor shaft 18 into bearing assemblies mounted into the two end plates 14, 16 as the end plates are assembled over the opposite end surfaces of the stator assembly 12.
In assembling the end plates 14, 16 to the opposite end surfaces of the stator assembly 12, the stator fastener holes 38 are aligned with end plate fastener holes 40 provided in each of the end plates. The end plates 14, 16 are secured to the opposite end surfaces of the stator assembly 12 by bolts 26 inserted through the aligned fastener holes of the stator and the end plates and by the nuts 28 screw threaded on the projecting ends of the bolts. However, before the bolts 26 are inserted through the aligned holes of the end plates and the stator assembly, the ground connector 24 is first positioned between the stator assembly and one of the end plates in its position shown in FIG. 1. The ground connector tab 48 is inserted between the stator 12 and the one end plate 14 with its tab hole 50 aligned with a fastener hole 38 of the stator and a fastener hole 40 of the end plate. The bolts 26 are then inserted through the aligned holes and the nuts 28 are screw threaded on the projecting ends of the bolts and tightened down.
The installation of the prior art ground connector 24 requires the manual positioning of the connector tab 48 with the tab hole 50 coaxially aligned with one of the stator fastener hole 38 while also manually positioning the two end plates 14, 16 on the opposite end surfaces of the stator and inserting a fastener bolt 26 through the aligned holes of the end plates, the stator and the ground connector tab. The positioning of these components while aligning the hole of the ground connector tab with the stator fastener hole and the end plate fastener hole before inserting the bolt through the aligned holes is both time consuming and cumbersome for the motor assembler.
The disadvantages in the prior art motor discussed above could be overcome by a ground connector that could be installed in the terminal block. The terminal block would securely hold the ground connector relative to the terminal block and would position the tab hole of the ground connector over a stator fastener hole when the terminal block is attached to the stator. This would eliminate the need for the motor assembler to hold the ground connector tab in position while securing the two end plates to the opposite end surfaces of the stator with the bolt and nut fastener, thus greatly simplifying the assembly of the electrical device and permitting automated assembly of the device.
The present invention provides a grounding system for an electrical device where a ground connector is securely held by a terminal block of the device and the ground connector is properly positioned relative to other component parts of the electrical device for making a grounding connection with those other component parts when the terminal block is assembled to one of the component parts. The invention is basically comprised of a modified terminal block and a ground connector that is designed to be assembled to the terminal block and securely held by the terminal block.
The terminal block of the invention is, for the most part, similar to prior art terminal blocks in that it is constructed of an electrically insulating material and includes a plurality of plug sockets that securely hold electrically conducting plugs of the electrical device. The terminal block is assembled to a side of the electrical device where it positions the conductive plugs where they can be easily connected to mating receptacles of a separate electrical connector that is attached to the terminal block. The terminal block of the invention differs from prior art terminal blocks in that it is provided with a socket designed to received and securely hold the ground connector of the invention.
The ground connector socket extends from a back surface of the terminal block to its front surface and is positioned on the terminal block in line with the other plug sockets of the terminal block and adjacent one side of the terminal block. The ground connector socket has a cross-section configuration that resembles two diametrically opposite quarter circles. A recessed slot intersects the ground connector socket at the back surface of the terminal block.
The ground connector is formed of a single monolithic piece of electrically conductive material. The ground connector has a length with a ground plug at one end and a connecting tab at its opposite end with a span of the ground connector connecting the ground plug and the tab. The tab is flat and has a hole passing therethrough for receipt of a threaded fastener of the electrical device. The tab projects from one end of the span of the ground connector and is positioned perpendicular to the span of the ground connector. The plug is also flat and projects from an end of the connector span opposite the tab. The plug has a series of barbs adjacent its connection to the span. The plug projects perpendicularly from the span and both the plug and the tab are positioned in parallel, horizontal planes although not in the same horizontal plane.
The plug of the ground connector is inserted into the terminal block ground connector socket from the back of the terminal block. However, because the mounting posts of the terminal block are also positioned at the back of the terminal block, the ground connector plug cannot be inserted directly into the ground plug socket of the terminal block due to the length of the span connecting the ground connector plug to the tab. The ground connector plug is first inserted into the ground connector socket of the terminal block from the back of the terminal block with the span of the ground connector positioned generally parallel with the adjacent mounting post of the terminal block. The ground connector plug is inserted a sufficient distance into the ground connector socket of the terminal block until the span of the ground connector is positioned generally between the back of the terminal block and the adjacent mounting post. In this position of the ground connector it can be rotated 90xc2x0 causing the span of the ground connector to be positioned between the back of the terminal block and the adjacent mounting post of the terminal block. Once in this position the ground connector plug is inserted to its full extent into the ground connector socket of the terminal block. The ground connector plug barbs are inserted into the recessed slot in the back of the terminal block as the ground connector plug is inserted completely into the ground connector socket of the terminal block. The barbs engage in the material of the terminal block as they are inserted into the recessed slot, thereby securely holding the ground connector to the terminal block.
With the ground connector plug completely inserted into the ground connector socket of the terminal block and with the barbs of the plug engaging in the material of the terminal block slot, the span extends across the back of the terminal block between the back of the terminal block and the mounting plug of the terminal block to the tab which is positioned by the span to one side of the terminal block. With this positioning of the tab by the span, when the terminal block is attached to the stator by inserting the terminal block mounting posts into the post holes of the stator, the span of the ground connector positions the tab over an end surface of the stator with the tab hole aligned coaxially with a fastener hole of the stator. In this position of the tab it provides a ground connection between the stator and an end plate of the electrical device that is attached to the surface of the stator the tab overlaps. The threaded fasteners passed through the fastener hole of the stator and the end plate hole with which the tab hole is aligned securely holds the tab between the stator and end plate. In this manner, the ground connector provides an electrically conductive ground connection between the stator and the end plate. Furthermore, with the ground connector securely held in the terminal block, the ground connector tab hole is held in alignment with the stator fastener hole and the end plate fastener hole by the terminal block being attached to the stator. Thus, the construction of the terminal block and the ground connector simplifies the prior art connection of a ground connector to an electrical device and also provides for automated assembly of the ground connector to the electrical device.